Known examples of structures for tightly joining a foundation and a column installed upright on a groundsel installed on the upper face of the foundation with each other in a wooden building, such as a wooden residential building, include, for example, structures in which an upper-end male screw portion of an anchor bolt projecting from the upper face of a foundation is fastened to a hold-down hardware piece attached to a side face of the base portion of a column. Unfortunately, such a hold-down hardware piece attached to the side face of a column base portion may be problematic; e.g., the hold-down hardware piece may hinder the attaching of a diagonal beam, or may constitute a heat bridge. For this reason, a column base joint structure in which column base fittings for tightly joining a column with an anchor bolt are embedded respectively in the column's base portion and a groundsel has been developed as a structure that replaces the hold-down hardware piece (e.g., see JP3488870 B).
In the column base joint structure disclosed in JP3488870 B, the column base fitting is constituted by: a cylindrical groundsel-embedded portion that is embedded in a groundsel and is tightly joined to an anchor bolt; and a tenon portion—which is provided separately from the groundsel-embedded portion—that has a columnar engaging portion projecting downward and is fixed to a bottom face portion of a column. After the groundsel is installed on the upper face of a foundation, the engaging portion of the tenon portion projecting from the column's bottom face portion is fitted into the groundsel-embedded portion, and thereby, a connecting hole formed in the engaging portion of the tenon portion is aligned with a connecting hole formed in the groundsel-embedded portion in a state where the column is installed upright on the groundsel, and the anchor bolt and the column are tightly joined with each other by hammering a locking pin into the connecting holes.